Basic and Applied Sciences in Obstetrics and Gynecology
Core concepts
A candidate must connect structure to clinical consequence. Pelvic anatomy: the ureter crosses the pelvic brim anterior to the bifurcation of the common iliac artery, then runs under the uterine artery about 2 cm lateral to the cervix-the classic “water under the bridge.” Lymphatic drainage of the ovary follows the ovarian vessels to para-aortic nodes, whereas the vulva drains to superficial inguinal nodes. Embryology: the Müllerian ducts form the fallopian tubes, uterus, cervix, and upper vagina; the lower vagina derives from the urogenital sinus. Disorders of Müllerian fusion explain septate, bicornuate, and didelphys uteri. Genetics: autosomal recessive risk, X-linked patterns, and the difference between numeric and structural chromosomal abnormalities. Physiology: the two-cell, two-gonadotropin model; progesterone withdrawal; and pregnancy-induced changes in plasma volume, GFR, and drug clearance. Pharmacology: hepatic CYP induction, renal clearance, and placental transfer determine dosing.
Traps
Questions love the ureter’s relation to the uterine artery during hysterectomy, the difference between round and ovarian ligaments, and the timing of organogenesis (weeks 3–8, when teratogens matter most). Do not confuse the urogenital sinus with the Müllerian system. In genetics, remember that an unaffected sibling of a child with an autosomal recessive condition has a 2/3 carrier risk, not 1/2.
Worked example
A couple has a child with cystic fibrosis (autosomal recessive). Their next child’s risk is 1/4. Their healthy child’s carrier probability is 2/3. If the population carrier frequency were 1/25, a healthy sibling’s risk could be refined with Bayesian analysis, but the 2/3 figure is the examination starting point.
Rule of thumb: draw the pelvic side wall and trace the ureter from the brim to the bladder; if a structure crosses it, name the structure before naming the operation.